Michelin and Dunlop have brought new hard compound tires to Circuit of The Americas for Porsche GT Team and Aston Martin Racing, respectively, as part of the "Joker" rule which permits one change of compound per season in GTE Pro.

Michelin's new tire will be used on Porsche's new 911 RSR, for the rest of the 2017 season, with the primary focus on the updated compound concerning longevity, although Michelin told RACER that it may affect its performance.

The reason for the change is because the French tire manufacturer concluded after the opening rounds of the season Porsche's 911 RSRs were at a disadvantage with the hard tires, which were dropping off toward the end of a double stint. The new compound allows Porsche's new GTE challenger to be on more of a level playing field with its fellow Michelin-shod rivals in the class, Ferrari and Ford.

It's not a brand-new compound though, as Michelin explained to RACER that Porsche had already tested it over the winter months prior to the current season, but initially chose the other option. However, as the new 911 RSR has evolved over the course of its debut season, Porsche and Michelin requested to the FIA back in July that it wanted to switch to the other compound.

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Meanwhile, Aston Martin Racing is also known to be using a "Joker" tire in Austin, from its technical partner Dunlop. The new compound for the British team replaces the third choice presented at the start of the season, an option understood by RACER to have been created as a conservative compound, developed to offer certainty over a double stint.

The original tire though, was found by Dunlop to have gone too far in one direction; the replacement being deemed far more useful in the operating window during the 6-hour races, which this season, has seen the amount of sets available to teams in qualifying and the races reduced to four, from six.

The new compounds from Dunlop and Michelin will be the only change of in GTE Pro this season, as the regulations only allow a single 'Joker' tire to be employed by each supplier. Therefore, Ford and Ferrari will continue to use the same sets of tires that they've used all season so far.